Somewhat unusually for North America, the fossil history of Connecticut is limited to the Triassic and Jurassic periods: there's no record of any marine invertebrates dating to the earlier Paleozoic Era, nor even any evidence of the giant megafauna mammals of the later Cenozoic Era. Fortunately, though, early Mesozoic Connecticut was rich in both dinosaurs and prehistoric reptiles, of which the Constitution State has numerous examples, as you can learn by perusing the following slides. (See a list of dinosaurs and prehistoric animals discovered in each U.S. state.)
Biodiversity Heritage Library/Flickr/CC BY 2.0
When its scattered fossils were unearthed in Connecticut, way back in 1818, Anchisaurus was the very first dinosaur ever to be discovered in the United States. Today, this slender plant-eater of the late Triassic period is classified as a "sauropodomorph," or prosauropod, a distant cousin of the giant sauropods that lived tens of millions of years later. (Anchisaurus may or may not have been the same dinosaur as another prosauropod discovered in Connecticut, Ammosaurus.)
Not a dinosaur at all, but a type of prehistoric reptile known as an anapsid (it's also technically referred to by paleontologists as a "procolophonid parareptile"), the tiny Hypsognathus prowled the swamps of late Triassic Connecticut about 210 million years ago. This foot-long creature was notable for the alarming-looking spikes jutting out of its head, which probably helped to deter predation by the larger reptiles (including the early dinosaurs) of its semi-aquatic habitat.
Superficially resembling scaled-down crocodiles, aetosaurs were a family of archosaurs dating to the middle Triassic period (it was a population of archosaurs that evolved into the first true dinosaurs about 230 million years ago, in South America). Specimens of Aetosaurus, the most primitive member of this breed, have been discovered all over the world, including the New Haven Formation near Fairfield, Connecticut (as well as in various other states of the union, including North Carolina and New Jersey).
Various Dinosaur FootprintsIvan / Getty Images
Very few actual dinosaurs have been discovered in Connecticut; that's decidedly not the case with fossilized dinosaur footprints, which can be viewed (in abundance) at Dinosaur State Park in Rocky Hill. The most famous of these prints have been attributed to the "ichnogenus" Eubrontes, a close relative (or species) of Dilophosaurus that lived during the early Jurassic period. (An "ichnogenus" refers to a prehistoric animal that can only be described on the basis of its preserved footprints and track marks.)